The present invention is directed to a device for fixing, on a spectacle lens, a mounting block for mounting the lens on the lens holder of an edging or bevelling machine.
Said mounting block can be, for example, the block described in French Patent application No. 76 14 905, filed on May 18th 1976, in the name of the applicant, or a similar block, flexible or rigid, adapted to be engaged on a spindle of an edging or bevelling machine.
The known blocks are provided on their blocking surface with an adhesive coating for fixing them onto the spectacle lenses and on the opposite surface with orienting and driving means adapted to cooperate with the complementary means of the spindle of the edging or bevelling machine.
An Apparatus, commercially available from the 3 M Company under the name of "3 M Brand EAP Blocker" enables such mounting blocks to be affixed to spectacle lenses.
This known apparatus is provided with fixed means for holding and positioning the mounting block, said means being similar to those of the spindle of the edging or bevelling machine.
The apparatus is further provided with fixed luminous marks for correctly positioning the lens, opposite to the block, before placing the block on the lens. Centering marks adapted to be put into coincidence with those of the apparatus are previously marked on the lens, generally on its convex surface onto which the block will be fixed.
The operator holds the lens between his fingers, above the mounting block, positions and orients it properly in relation to the luminous marks, then applies the lens onto the block. It is difficult to carry out these operations because the operator has no support for the lens, which frequently causes significant centering errors.
Another apparatus is also known, which is used only for fixing a suction cup onto a lens. It is provided with a fixed suction cup holder and a movable lens having centering marks consisting of engraved lines.
The marks on the lens are made to coincide with those on the holder, then while maintaining the lens correctly on its holder; pressure is applied on the assembly in order to fix the suction cup on the lens. The apparatus is more convenient than the one previously described; however both present the same major drawback: the centering marks, luminous marks or engraved lines are fixed and placed in a single common plane.
The marks on the lens are disposed on one of its surfaces and are at a distance from the plane of the marks on the apparatus, said distance being more or less large according to the curvature of the marked surface of the lens. This can result in significant parallax errors and therefore in a defective positioning of the mounting block on the lens.